A Foreign Office minister has described the attempted murder of a former Russian spy as “the most dastardly heinous act we’ve seen on European soil since 1945”.

Sir Alan Duncan told Radio 4’s World at One that “by expelling the largest number of diplomats for many decades, it shows to the world, and to Russia in particular, that we are taking firm steps” over this issue.

Theresa May had earlier told MPs that 23 Russian diplomats identified as “undeclared intelligence officers” have been given a week to leave and that high-level contact with Moscow would be suspended.